Approximately 22% of youth currently smoke cigarettes despite the increased risk of cancer and cardiovascular disease associated with cigarette use. Tobacco use continues to be the leading, preventable cause of mortality among US adults. Research has shown that those who smoke their first cigarette between the ages of 14-26 are more likely to become nicotine dependent, and, therefore, more resistant to smoking cessation efforts, than those initiating smoking at a later age. Although the smoking prevalence among girls declined in the 1970's and 1980's, the current smoking rates among high school girls has held constant from 1998 to 2000. Despite the negative health consequences associated with smoking, weight concerns and fear of weight gain have been shown to be associated with the uptake of smoking in girls. Alternatively, exercise has been shown to be a positive health behavior, and can provide the same perceived benefits of smoking: self-esteem, relaxation, weight management. In previous trials in adult women, vigorous intensity exercise has been shown to be effective for aiding with smoking cessation. Therefore, this study will adapt the efficacious group-based cognitive behavioral smoking cessation treatment plus exercise to meet the needs of adolescent girls. This project will consist of two phases. In Phase I of this project, 4 focus groups will be conducted (each consisting of 8-10 adolescent girls) to adapt the intervention. Adaptations will include making the materials, intervention content, and language age-appropriate and relevant for youth. Phase II of the project will consist of a randomized pilot study in which 40 adolescent girls will be randomly assigned to: a) standard cognitive-behavioral smoking cessation plus exercise (CBT+Exercise) or b) standard cessation with equal contact time (Standard+Contact). The sample will be recruited, treated for 12 weeks and followed for 3 months. Smoking cessation outcome (continuous abstinence) will be validated by saliva cotinine. Exercise adherence will be validated by attendance at supervised sessions, and objective monitoring. Secondary analysis, of proposed theoretical mediators of behavior change will be conducted, including weight concerns and self-efficacy. The primary hypothesis is that girls in the CBT+Exercise group will have higher quit rates than girls in the Standard+Contact group. In summary, we seek to:1) conduct the formative work to adapt the cessation materials and exercise protocol from a focus on adult women to adolescent girls, and 2) conduct a small randomized pilot trial to determine the preliminary efficacy of the intervention in a sample of adolescent girls. Therefore, this study will serve as a pilot for a larger clinical trial. Successful smoking cessation in adolescent girls could contribute to the future reduction of chronic disease mortality in this group.